Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$17.33	6.772%	$18.5036	$18.50	$18.50	$18.50
Purchase #2	$91.35	7.779%	$98.4561	$98.46	$98.45	$98.50
Purchase #3	$127.49	10.138%	$140.4149	$140.41	$140.40	$140.40
Purchase #4	$45.75	7.782%	$49.3103	$49.31	$49.30	$49.30
Purchase #5	$182.39	5.563%	$192.5364	$192.54	$192.55	$192.50
Purchase #6	$19.50	12.521%	$21.9416	$21.94	$21.95	$21.90
Purchase #7	$238.53	13.823%	$271.502	$271.50	$271.50	$271.50
7 purchase totals =	$722.34		$792.6649	$792.66	$792.65	$792.60